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File Access Methods in OS

Last Updated on March 15, 2023 by Prepbytes

In the modern world, computing power has increased many folds and because of that the data is an essential component and is stored in a variety of formats among all the formats the file is one of the formats that is accepted and used everywhere and in every aspect of computing. So the operating system must provide efficient methods to access files so that we can easily use the data and manipulate it accordingly. While moving further in this article we will learn all about file access methods in os with brief explanations of all the methods, including their benefits and drawbacks.

What are File Access Methods in OS?

The file can be referred to as the collection of data which is in the form of bits/ bytes which are stored in secondary storage like hard drives. File access methods in OS refer to the techniques used to access read and write data from and to a file. There are various file access methods in os like:

  • Sequential Access
  • Direct Access
  • Indexed Access

All the above file accessed methods in OS have their own benefits and drawbacks which are discussed further in this blog. We can use any of the above-mentioned file access methods in OS depending upon the intended use of data the storage medium, and the type of data being stored.

Sequential Access

Sequential access is one of the simplest and oldest file access methods in OS. In this, the data is accessed in sequential order, one record at a time. This is useful for log files or media files as they are large files and the file is processed by accessing the data sequentially. We do not have to keep the track of the location of the data as the data is accessed sequentially. In this method, the data is read from the beginning of the file until the desired result is found.

It is used in devices like tapes as they have continuous steam of data and the data is written and read sequentially. In the sequential file access method in OS, the data is stored on disk or tape in a continuous block, and each of the records is accessed in the proper order. The position of the tape is changed at each round.

We can also use this in batch mode. But sometimes it can be slow for large files where the data is accessed randomly because if the record needs to be modified or deleted, the entire file needs to be written.

Advantages of Sequential Access
Here are some of the advantages of the sequential file method access in OS.

  • It is very simple to implement as the data is read from the beginning until the desired result is found.
  • It is very efficient for reading a large file.
  • Used to read the continuous stream of data.
  • The overhead is low.

Disadvantages of Sequential Access
Some of the disadvantages of sequential access are given below:

  • It is comparatively slow for random access of the data as it only requires reading the data sequentially so it will not work fast in the case of randomly distributed data.
  • It will face difficulty in managing the fragmented data as in this case it will result in wasted storage space.
  • It is inefficient for writing large files where the data needs to be modified or added as we have to rewrite the entire record if the data needs to be modified or deleted.
  • It is limited to single-user access is multiple users try to access the same file sequential access will create a conflict.

Direct Access

It is also known as the random access method this is one of the file access methods in OS and is used to read and write the data in a non-sequential order. We can access the data directly by specifying the location of the data on the storage medium. It is commonly used in solid-state drives, hard disks, and the flash drives, where the data is stored in blocks or sectors and each of the blocks or sectors is accessed using a unique address.

Direct access allows reading the data randomly through any point without reading all the preceding data. And this feature makes it very useful and efficient in large files as we can access any specific data within the large file, and it is often used in real-time systems where data needs to be accessed quickly.

Advantages of Direct Access
Here are some advantages of direct access:

  • We can use direct access for processing large files where the data is not accessed sequentially.
  • It is faster than sequential access as here only the desired result is written or read.
  • It is efficient in indexing structures like B-tress as they allow efficient access to data in large files.
  • It also provides multi-user access.

Disadvantages of Direct Access
Some of the disadvantages of direct access are given below.

  • It has a higher overhead compared to sequential access as we need to determine the location of data before accessing it.
  • Reading the data sequentially can be time-consuming.
  • Sometimes it leads to fragmentation which will automatically lead to wastage of storage and hence the reduction in performance.

Indexed Access

As the name suggests the indexed access method is one of the file access methods in OS that uses the index to locate the data within a file. In this method, we will create an index that will contain the address of all the data blocks within the file. When a user request to access any part of the data the request is first passed to the index with the help of the index will find the address of that data block and will locate it, then the block is read forms the storage medium.
It provides an efficient way to access all the data blocks or records within a large file without having to search the entire file for the data. This method is commonly used in database management systems where efficient and quick access to records is required.

Advantages of Indexed Access
Some of the advantages of indexed access are given below:

  • It provides fast access to all the data blocks within the file as we can directly locate the data block easily.
  • It is very efficient for large files as it saves a lot of searching time.
  • It has better memory management as it allocation space to the index and data blocks separately. And this will prevent memory overflow.
  • It will improve data integrity by maintaining a separate index for each file.

Disadvantages of Indexed Access
We have explained some of the disadvantages of indexed access below:

  • There can be index overhead with creating and maintaining the index. As we have to update the index every time a record is modified or updated.
  • The storage requirements increase as the additional storage space to store the index
  • The concurrent access is limited as multiple users cannot modify the same index simultaneously.
  • The complexity will increase due to the addition of an index in the file management system.

In summarizing the file access methods in OS are very crucial components. They allow efficient retrieval, storage, and manipulation of data in files. The choice of file access methods in OS depends on the user and the structure and size of the data being stored. All of the file access methods in OS have their own use cases based on their advantages and disadvantages. As some of them are used for sequential access whereas some are for direct access and for getting the address we can also use the indexed method.

Frequently Asked Questions

Here are some of the frequently asked questions about the file access methods in OS.

1. What is disk fragmentation in Operating System?
When free memory on a disc is dispersed throughout the disc, it is challenging to assign contiguous chunks of memory for new files. This situation is known as disc fragmentation.

2. What do you understand by File Control block?
An operating system uses a file control block as a data structure to keep details about a file, including its location, size, and access rights.

3. What is a file descriptor?
An computer system uses a file descriptor as a data structure to describe an open file. It includes details about the file, including its position, size, and entry rights.

4. How is file access controlled by the computer system?
By regulating file access through methods like access control lists (ACLs) and file permissions, the operating system controls file access. By supplying file system calls that let processes create, read, write, and delete files, it also controls file access requests.

5. What is file sharing?
The capacity for numerous processes or users to view the same file at once is known as file sharing. In order to prohibit numerous processes from simultaneously viewing the same file, the operating system implements file-locking methods. It also provides file-sharing protocols like Server Message Block (SMB) or Network File System (NFS).

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